The present invention relates to a compressed-air-operated disc brake, in general and more particularly for use in commercial road vehicles.
Compressed-air-operated or pneumatic disc brakes of the above-mentioned type are known, for example, from German Patent Documents DE-OS 37 16 202, DE-OS 40 32 885 as well as DE-OS 42 12 384 which is not a prior publication. In the case of these known disc brakes, a caliper reaches around the brake disc, which caliper is disposed so that it can be displaced in the axial direction. On one side of the caliper, a compressed-air-operated application device is arranged during whose operation a brake shoe situated on this side of the brake disc is pressed against the friction surface of the brake disc. Whereupon, the caliper is displaced in the opposite direction because of the reaction forces and, as a result, a brake shoe situated on the opposite side also presses against the brake disc.
In the case of these known disc brakes, the application device has a rotary lever as an actuating element which is disposed so that it can be swivelled about an axis of rotation extending in parallel to the plane of the brake disc. On its side facing the brake disc, the rotary lever rests by means of an eccentric approximately in the longitudinal center on a transverse element which extends in parallel to the axis of rotation. The traverse element is displaceably guided with respect to the brake disc. Two adjusting spindles, which are provided with an external thread, are adjustably screwed in a parallel arrangement in a respective assigned internal thread of the transverse member. Because of the use of two adjusting spindles, such an application device is also called a "two-spindle" application device.
The two adjusting spindles each include of a pressure member disposed on their brake-disc-side end upon the brake shoe which is disposed on the application side in the caliper so that the caliper can be displaced with respect to the brake disc. By at least one adjusting device which is coupled in an axially displaceable but non-rotatable manner with one of the two adjusting spindles and, during each actuation of the rotary lever, acts by way of a sliding clutch on the respective adjusting spindle, the ventilating play, which changes because of the wear of the lining, maintains its correct desired value in a constant manner. The rotation of the mentioned adjusting spindle which is caused by the adjusting device in the case of a lining wear, is transmitted by a synchronizing device to the other adjusting spindle such a that this adjusting spindle is rotated by the same angle and therefore reduces its distance from the brake disc by precisely the same distance.
In the simplest case, only one actuator is arranged in the above-mentioned second adjusting spindle, which actuator couples this adjusting spindle in a non-rotatable manner with the synchronizing device. The actuator may be constructed, for example, of a gear wheel which meshes in an internal toothing of the adjusting spindle and which is coupled with the synchronizing device by a shaft. However, for the second adjusting spindle, a separate adjusting device may also be provided. In this case, twice as much adjusting forces is achievable, but with correspondingly higher manufacturing costs. Also when two adjusting devices are used, a synchronizing device will still be necessary because an exactly synchronous method of operation of both adjusters will still be absolutely required for ensuring a uniform abrasion of the brake lining and prevent the occurrence of a circumferential diagonal wear, that is, the non-uniform wear of the brake linings in the tangential or circumferential direction of the brake disc.
In the currently most customary embodiment, the synchronizing device of the known application devices consists of a toothed belt or a link chain coupled with a gear wheel of the adjusting device and another gear wheel of the actuator or of the other adjusting device so that a belt wrap transmission is formed. As an alternative, it is also known to replace the toothed belt or the link chain by an uneven number of interposed gear wheels. However, because of the numerous required bearings, this solutions results in high expenditures and is therefore correspondingly expensive.
The gear wheels, which are coupled with the respective adjusting device and/or actuator, are provided in customary embodiments on the end of these function elements which faces away from the brake disc so that an "exterior" synchronizing device is formed. Although such an exterior synchronizing device permits a very good access and therefore an easier maintenance, several additional covering components are required. This increase the manufacturing costs and, on the other hand, clearly increase the risk of a leakiness of the housing, which must be prevented in every case and is caused by the additional sealing points.
Therefore, for avoiding these problems, "interior" synchronizing devices have also been taken into consideration. The gear wheels of the adjusting device and/or of the actuator as well as the toothed belt or the chain are arranged approximately at the level of the eccentric of the transverse member. However, in this functionally important area of the application device, this arrangement creates considerable space problems so that an enlargement of the housing dimensions may be unavoidable. Furthermore, the maintenance is considerably more difficult than in the case of an exterior arrangement of the synchronizing device.
It is an object of the invention to provide a compressed-air-operated disc brake whose synchronizing device is distinguished by a space-saving construction and high serviceability while avoiding any leakage problems.
According to the invention, this synchronizing device therefore consists of a shaft which extends essentially in the area of the axis of the eccentric and which has a bevel gear on each face which meshes with a corresponding bevel gear of the adjusting device or actuator so that a corresponding angle drive is formed. This shaft, which replaces the toothed belts or link chains customary in the state of the art, requires no additional space so that the synchronizing device can be installed without any significant influence on the space conditions in the interior of the application device. Furthermore, the shaft is constructively simpler than a toothed belt or a link chain so that, just for this reason, servicing operations will be required much less frequently. Finally, no leakage problems are caused by the arrangement of the synchronizing device according to the invention.
If, corresponding to the first embodiment of the above-mentioned German Patent Documents DE-OS 42 12 384, the complete content of which is, incorporated herein by reference the eccentric of the application device is formed by a roller which rests in the transverse and in the rotary lever in a respective shell-shaped bearing surface, it is particularly advantageous for this eccentric roller to be simultaneously used as the shaft of the synchronizing device. The reason is that the synchronizing device can then be produced in an extremely cost-effective manner because the eccentric roller must only be modified by providing corresponding bevel gears which--a one-piece construction with the eccentric roller. Otherwise, only the two bevel gears are required for the adjusting device or the actuator.
This embodiment of the synchronizing device according to the invention is also distinguished by two other advantages: On the one hand, in the preferred embodiment, the lateral bevel gears protrude by a certain distance so that an axial securing of the eccentric roller on the traverse member is achieved. On the other hand, any undesirable change of the position of the two adjusting spindles, which is the result of vibrations or the like, is reliably prevented by the eccentric shaft, specifically without the requirement of an additional braking device. This positive effects is a result of the fact that, also in the inoperative condition of the brake, the transverse is prestressed by a pressure spring in the direction of the rotary lever so that the eccentric shaft is prevented, by corresponding friction forces from carrying out an automatic rotation. Nevertheless, the adjusting torque exercised on the adjusting device is completely sufficient at any time for overcoming these friction forces so that the eccentric roller operating as the synchronizing device, does not impair the reliable adjustment. It is only when the ventilating play of both brake shoes is completely overcome, that so much force is applied that the eccentric roller can no longer be rotated because the transverse-side bearing surface has a much higher coefficient of friction than the lever-side bearing surface. However, at this point in time, no adjusting movement is desired and this effect is more an advantage then a disadvantage.
If nevertheless a complete decoupling of the synchronizing device from any friction forces should be desired, or if these has advantages for other reasons, the eccentric roller may be constructed as a tube-shaped part whose internal bore is used as a bearing of a correspondingly constructed shaft on whose faces one bevel gear respectively is fastened, for example, by screwing.
If, corresponding to the additional embodiments of the above-mentioned German Patent Document DE-OS 42 12 384, the eccentric of the application device is, in contrast, constructed in one piece with the traverse or with the rotary lever, a longitudinal bore is formed in the eccentric which is used for the bearing of the shaft of the synchronizing device. Operationally, this type of construction or bearing corresponds to the above-explained use of a hollow roller for the eccentric disposed on both sides.
If permitted by the installation space and particularly by the implementable diameter of the eccentric constructed in one piece with the traverse or with the rotary lever as well as by the respective diameter of the synchronizing shaft, it may be advantageous to arrange the longitudinal bore eccentrically with respect to the longitudinal axis of the eccentric, specifically in a preferred manner concentrically with respect to the axis of rotation of the rotary lever. This measure has the advantage that, when the rotary lever is actuated, the synchronizing shaft disposed in this longitudinal bore will hardly or not at all change its axial relative position with respect to the bevel gears of the adjusting device or the actuator. As a result, these bevel gears will continue to mesh with those of the shaft even if the transverse member and therefore the eccentric move toward the brake disc when the rotary lever is actuated.
It should be pointed out, however, that, as proven in tests, such a partial reduction of the mutual meshing of the bevel gears forming the angle drive is not important in practice, in the case of a suitable dimensioning. This is because an adjustment which may already be initiated by the adjusting device will be transmitted to the other adjusting spindle no later than when the traverse member rerotarys into its inoperative position 4 since then the bevel gears will then again be in a complete engagement. Thus, this effect also causes no problem in the case of the above-described synchronizing devices since the synchronizing movement is transmitted by the eccentric roller or a shaft disposed in this roller and no such displacement of the axis of rotation of the shaft can be implemented.
Nevertheless, a continuously good meshing of the bevel gears can also be achieved in the case of such a shifting of the location of the axis of the synchronizing shaft (eccentric roller or shaft disposed in it) if the bevel gears of the adjusting device or of the actuator are fastened to it in an axially displaceable manner so that, possibly with the additional use of a spring element, a following of these bevel gears can be achieved with respect to those of the shaft.
Additional further developments of the invention may, for example, be the additional use of a slide bearing for the synchronizing shaft the use of plastic material for the bevel gears.
In the following the invention will now be explained in detail by the description of embodiments with reference to the drawing.